Trisomy 18

Trisomy 18 is a chromosomal abnormality due to an extra copy of chromosome 18. The prognosis is extremely poor. It was first described by Edwards in 1960. The incidence is approximately 1:3000 to 1:7000 in live births. A variety of sonographic and MRI abnormalities are seen in fetuses with trisomy 18 including:

Case Report

These are two cases of trisomy 18. The first one is a 40-year-old patient, G2P0, referred to our service at 18 weeks. The ultrasound showed an association of Arnold-Chiari II and valve of posterior urethra (Figures 1 to 8). An amniocentesis was performed and confirmed the karyotype (47,XY+18). The parents decided to interrupt the pregnancy.

Note the dilatation of the bladder and proximal urethra.

Same view with 3D.

Axial view of the cranium showing the "lemon" sign (left image) and the "banana sign" (right image) at 18 weeks.

Left image: Note the meningocele (red arrow) and the dilatation of the bladder (blue arrow). Right image: Note the dilatation of the bladder (red arrow).

Case 2

This is a 31-year-old, G1P0, with a fetus in the first ultrasound examination with multiple malformations. These are the ultrasound images at 12, 18, 21 and 25 weeks. At 21 weeks, a MRI was performed.

3D view showing the abdominal defect. In the 2D image, note the view at the level of the orbits and the herniated liver (red arrow).

Coronal T2 showing the small abdomen. The brains development looks normal.

View of the small placenta (arrow).

Ultrasound and sagittal T2 images of the superior limb reduction.

The malformations observed were:

“Strawberry” calvarium

cerebellar hypoplasia

ventricular septal defect and overriding aorta

liver herniation with normal insertion of the umbilical cord in the abdomen

superior limb reduction

left club foot

intrauterine growth restriction

The placenta was very small and the polyhydramnios was observed after the 21th week. The chorionic villi sampling was performed at 12 weeks and confirmed the karyotype (47,XX +18). The patient decided to continue the pregnancy but the fetus died intra utero at 26 weeks. The anatomopathology was not authorized by the parents.